Biochar (terra preta) is a charcoal created from biomass under controlled conditions to optimize its performance as a soil amendment. Char is widely believed to improve plant growth and general soil health via increases in soil microbial activity, increased water and mineral retention, increased soil organic matter, reduced need for fossil fertilizers, increased resistance to disease, and other potential mechanisms. Furthermore, the introduction of charcoal to soils is believed to reduce atmospheric green house gases by preventing CH4 and N2O release from decaying biomass, as well as through long-term removal of carbon from the carbon cycle via underground sequestration as stable charcoal. When charcoal production is combined with energy generation (e.g., through biomass gasification), the total energy and soil cycle is carbon negative. Power is generated and soils are improved, while simultaneously drawing down atmospheric GHG levels.
Pyrolysis, the method used to create charcoal, is currently heavily used in industrial plants to produce a variety of products. However, consumers, particularly those consumers who can both produce biomass and utilize char, rarely utilize these industrial plants to convert their biomass to char. This is due to access, transportation, and convenience issues. Furthermore, the large size and expense of running a pyrolysis plant generally prevents consumers from building or purchasing one of their own. Instead, the consumers dispose of the biomass in other ways, such as burning, that do not reclaim the energy stored within the biomass, nor the minerals or carbonaceous matter that would otherwise be of benefit to soils.
Gasifiers present an appealing solution to this issue, as gasifiers utilize pyrolization in the production of syngas, and produce charcoal as an intermediary to syngas. Furthermore, gasifiers (such as that described in U.S. application Ser. No. 12/846,807, incorporated herein in its entirety) can be scaled down for consumer use. However, consumer gasifiers currently do not have an effective means of interrupting the gasification process to remove charcoal with characteristics appropriate for use as biochar. While typical downdraft gasifiers do have a charcoal and ash byproduct that remains after combustion and reduction, this charcoal is not ideal for use as biochar. More specifically charcoal collected post downdraft gasification has passed through the high temperatures of combustion and reduction in the hearth, which completely devolatilizes the charcoal. Biochar is typically believed to benefit from a lower temperature pyrolysis, so as to leave a portion of the volatiles in the char, which is useful nutrition for soil microbes. Furthermore, very little charcoal is typically left post hearth, as most has usually been consumed during reduction to produce gas, so post hearth collection does not produce the high volumes of charcoal usually desired.
Thus, there is a need in the biochar field to create a new and useful gasifier from which biochar can be removed. Moreover, there is a need in the biomass generator field to create a new and useful generator from which electrical power and biochar can be extracted simultaneously, and in variable ratios.